In 2009, standardization of 10G-EPON (10 Gigabit Ethernet Passive Optical Network: “Ethernet” is a registered trademark) in IEEE802.3av was completed. The 10G-EPON features transfer 10-times faster than GE-PON (Gigabit Ethernet Passive Optical Network: see non-patent literature 1) already in widespread use. In addition, the existing GE-PON and the 10G-EPON can be used in a coexistent state.
When using the GE-PON and the 10G-EPON in a coexistent state, the WDM technology that uses different wavelengths for a 1G downstream signal and a 10G downstream signal is used, and the TDM technology is used between 1G downstream signals and between 10G downstream signals. As for upstream signals, a 1G upstream signal and a 10G upstream signal use the same wavelength, and the TDMA technology is used for both the 1G upstream signal and the 10G upstream signal. That is, three different kinds of wavelengths are used for the 1G downstream signal, the 10G downstream signal, and the upstream signals.
FIG. 41 shows an example of the arrangement of a conventional 10G-EPON system. As shown in FIG. 41, in the 10G-EPON, the GE-PON and the 10G-EPON can be used in a coexistent state. For this reason, 1G-ONUs (Optical Network Units) and 10G-ONUs can be connected to one OLT.
FIG. 42 is a block diagram showing the arrangement of an OLT for the conventional GE-PON (see patent literature 1). FIG. 43 is a block diagram showing the arrangement of the main part of frame transfer processing used in the OLT for the conventional GE-PON.
In the conventional OLT, a frame transfer processing unit 60 decides the destination ONU of the downstream frame by the destination MAC address of the downstream frame. To do this, a MAC address registration unit 61A registers the transmission source MAC address of a received upstream frame in a MAC address search table 61B in association with the LLID (Logical Link ID) of the transmission source ONU. A MAC address search unit 61C has a function of, when the destination MAC address of the received downstream frame is already registered in the MAC address search table 61B, judging the LLID associated with the MAC address as the destination ONU.
In the OLT shown in FIG. 42, a first transmission/reception circuit 52 is a circuit that transmits/receives a frame to/from the ONU via the PON connected to a PON port 51.
A second transmission/reception circuit 58 is a circuit that serves as an interface to a carrier network NW connected via an SNI (Service Node Interface) port 59 provided on the SNI side.
A frame demultiplexing unit 53 is a processing unit that transmits, out of frames received by the first transmission/reception circuit 52, a frame (control frame used to control the PON) for an OLT 50 to a control frame processing unit 54 and transmits the remaining frames to the frame transfer processing unit 60.
A frame multiplexing unit 56 is a processing unit that time-divisionally multiplexes a downstream frame from the frame transfer processing unit 60 and a control frame from the control frame processing unit 54 and transmits them to the first transmission/reception circuit 52.
The frame transfer processing unit 60 is a processing unit that transfers frames received from the frame demultiplexing unit 53 and the second transmission/reception circuit 58 based on their destination MAC address.
The control frame processing unit 54 is a processing unit that performs processes concerning PON control such as a discovery process for automatically assigning an LLID to each ONU and arbitration of an upstream signal (signal from an ONU to the OLT) and processing of transferring the PON-IF port information such as the LLID of each ONU to a band assignment processing unit 55.
The band assignment processing unit 55 is a processing unit that performs processing of assigning a band (transmission start time and transmission data amount) to an ONU or processing of managing PON-IF port information transferred from the control frame processing unit 54 in response to a request from the control frame processing unit 54.
Out of the frame transfer processing unit 60 shown in FIG. 43, a MAC address processing unit 61 registers/searches for a MAC address. In the MAC address processing unit 61, the MAC address registration unit 61A searches the MAC address search table 61B based on the transmission source MAC address of a received upstream frame. If the transmission source MAC address is not registered in the MAC address search table 61B, the MAC address is newly registered. If the transmission source MAC address is already registered in the MAC address search table 61B, the registered information is updated (if the registered information need not be updated, updating may be omitted).
The LLIDs of ONUs corresponding to the respective transmission source MAC addresses are registered in the MAC address search table 61B.
Based on the destination MAC address of a received downstream frame, the MAC address search unit 61C reads out a corresponding LLID from the MAC address search table 61B and decides the LLID to be given to the downstream frame.
A latency absorption unit 61D adds a delay to the received downstream frame, and absorbs the latency by the LLID decision processing of the MAC address search unit 61C.
An output synthesis unit 61E inserts the LLID decided by the MAC address search unit 61C into the preamble of the downstream frame output from the latency absorption unit 61D, thereby giving the destination LLID to the downstream frame to be transmitted.
In the 10G-EPON system, even when downstream frames for a 1G-ONU and a 10G-ONU coexist, the LLID of each destination ONU can similarly be decided. However, it is necessary to separately confirm what kind of ONU should have each LLID and transmit the frame from the downstream frame output of a corresponding rate. However, the conventional OLT does not have the function.
FIG. 44 is a block diagram showing the arrangement of the main part (after change) of frame transfer processing that can be considered as an example when adding, to the conventional OLT, the function of confirming the type of an ONU from an LLID and transmitting the frame for the downstream frame output of a corresponding rate. In the conventional OLT, when adding a circuit that decides the LLID of a destination ONU from the destination MAC address of a downstream frame, decides downstream transmission speed information from the LLID, and adds the pieces of information to the downstream frame (that is, when supporting 10G-EPON), the frame transfer processing unit 60 supposedly needs a downstream transmission speed processing unit 62 as shown in FIG. 44.
Referring to FIG. 44, a speed information registration unit 62A acquires the LLID of a transmission source ONU from the preamble of a received upstream frame, reads out downstream transmission speed information corresponding to the LLID of the transmission source ONU from the band assignment processing unit 55, and registers the downstream transmission speed information in a downstream transmission speed management table 62B in association with the LLID.
Downstream transmission speed information corresponding to the LLID of each ONU is registered in the downstream transmission speed management table 62B.
A downstream transmission speed search unit 62C reads out downstream transmission speed information from the downstream transmission speed management table 62B based on the destination LLID of a downstream frame and decides the downstream transmission speed information of the downstream frame to be transmitted.
A second latency absorption unit 62D adds a delay to the downstream frame having the added destination LLID, and absorbs the latency by the downstream transmission speed decision processing of the downstream transmission speed search unit 62C.
A second output synthesis unit 62E gives the downstream transmission speed information read out by the search of the downstream transmission speed search unit 62C to the downstream frame output from the second latency absorption unit 62D.
The downstream frame is sent to the PON at a given speed in accordance with the given downstream transmission speed information.
Note that in FIG. 44, an upstream frame and downstream transmission speed information from the band assignment processing unit 55 are input to the speed information registration unit 62A. However, the circuit (speed information registration unit 62A) for registration is not always necessary. Since software configured to control and manage the OLT 50 grasps the downstream transmission speed information corresponding to each LLID, necessary information can be written in the downstream transmission speed management table 62B by the software.